8.2.11 Flood overlay code

8.2.11.1 Application

(1) This code applies to assessing development in the Flood overlay, if:

(a) accepted development subject to compliance with identified requirements, where acceptable outcomes of this code are identified requirements in a table of assessment for an overlay (section 5.10); or

(b) assessable development where this code is an applicable code identified in the assessment benchmarks column of a table of assessment for an overlay (section 5.10); or

(c) impact assessable development.

(2) Land in the Flood overlay is identified on the Flood overlay map and is included in the following sub-categories:

(a) Brisbane River flood planning area 1 sub-category;

(b) Brisbane River flood planning area 2a sub-category;

(c) Brisbane River flood planning area 2b sub-category;

(d) Brisbane River flood planning area 3 sub-category;

(e) Brisbane River flood planning area 4 sub-category;

(f) Brisbane River flood planning area 5 sub-category;

(g) Creek/waterway flood planning area 1 sub-category;

(h) Creek/waterway flood planning area 2 sub-category;

(i) Creek/waterway flood planning area 3 sub-category;

(j) Creek/waterway flood planning area 4 sub-category;

(k) Creek/waterway flood planning area 5 sub-category;

(l) Overland flow flood planning area sub-category.

Editor's note—For the purposes of the overlay, the Pine and South Pine rivers are treated as Creek/waterway flood planning area sub-categories.

Note—The Flood overlay is a 'natural hazard area' for the purpose of the State Planning Policy. Within this area, susceptibility to flooding has been identified. The natural hazard area identified on the Flood overlay map may not reflect the full extent of the flood affected area.

Editor’s note—For a proposal to be accepted development subject to compliance with identified requirements, it must meet all the identified acceptable outcomes of this code that relate to the applicable sub-category and any other applicable code. Where it does not meet all identified acceptable outcomes, the proposal becomes assessable development and a development application is required. Where a development application is required, only the specific acceptable outcomes that the proposal fails to meet need to be assessed against the corresponding assessable acceptable outcomes or performance outcomes and relevant overall outcomes. Other identified acceptable outcomes that are met are not assessed as part of the development application.

(b) Provide for the assessment of the suitability of development in the Flood overlay.

(2) The purpose of the Flood overlay code will be achieved through the following overall outcomes:

(a) Development minimises exposure of people and property to unacceptable risk from flood hazard in all flood events.

(b) Development and infrastructure mitigates the flood risk through its location, siting, design, construction and operation whilst maintaining amenity.

(c) Development does not unduly burden the city's counter-disaster response capacity, including emergency services access during a flood emergency.

(d) Development provides for efficient evacuation and access for evacuation resources including emergency services during flood events, or otherwise plans for the prospect and impact of isolation or hindered evacuation during flooding.

(f) Development ensures that emergency management plans respond to the number and capacity of future users of the development to safely participate in emergency measures such as evacuation.

(g) Development ensures that essential building services or services essential for the development are designed, located and operated to minimise the flood risk to people, minimise damage to property, disruption to building function, and re-establishment time after a flood event.

(h) Development involving hazardous materials manufactured, handled or stored in bulk does not adversely impact on public safety and the environment as a result of the impacts of floodwater.

(i) Development does not, directly or cumulatively, cause or increase adverse impacts on other properties or land within the floodplain from flooding.

(j) Development and infrastructure mitigates the impacts of hydraulic hazard due to predictable future increases in rainfall intensity on flooding.

(k) Development prioritises, in order, the safety of people, protection of public infrastructure and protection of private property, in the management of the economic, social and environmental impacts of flooding.

8.2.11.3Performance outcomes and acceptable outcomes

Table 8.2.11.3.A—Performance outcomes and acceptable outcomes

Performance outcomes

Acceptable outcomes

Section A—If for accepted development subject to compliance with identified requirements (acceptable outcomes only) or assessable development for a dwelling house including any secondary dwelling

Note—Development for a dwelling house does not require assessment against any other sections of this code.

Development for a dwelling house and any secondary dwelling complies with the minimum flood planning levels in Table 8.2.11.3.B.

Note—If located in an area that has no flood level information available from the Council such as an overland flow path, a Registered Professional Engineer of Queensland with expertise in undertaking flood studies is to certify that the flood level and development levels for the dwelling house and any secondary dwelling achieve the required flood planning levels in Table 8.2.11.3.B.

AO1.3

Development involving a building undercroft complies with the minimum clearance requirements in Table 8.2.11.3.E.

(c) will not result in a material increase in flood levels or flood hazard on upstream, downstream or adjacent properties.

AO2

Development:

(a) is not located within the Creek/waterway flood planning area 1, 2 or 3 sub-categories or the Overland flow flood planning area sub-category; or

(b) provides an open undercroft area from natural ground level to habitable floor level for any area inundated by the defined flood event; or

Note—This undercroft area is not suitable for providing non-habitable rooms, secure storage of valuables, or future enclosing for storage or car parking. The clear area may include structural elements such as columns and floor substructure. The Flood planning scheme policy provides guidance on undercroft design.

Editor's note—An open undercroft design may be achieved through a 'valance' treatment around the perimeter of an otherwise internally clear undercroft.

(c) a report from a Registered Professional Engineer Queensland certifies that the development in the Creek/waterway flood planning area or Overland flow flood planning area sub-categories will not result in a material increase in flood level or flood hazard on upstream, downstream or adjacent properties.

Section B—If accepted development subject to compliance with identified requirements (acceptable outcomes only) or assessable development other than for a dwelling house or reconfiguring a lot

Note—If development that is accepted development subject to compliance with identified requirements complies with the acceptable outcomes of this part, no further assessment against this code is required.

(c) does not reduce the ability of evacuation resources including emergency services to access and evacuate the site in a flood emergency, with consideration to the scale of the development;

(d) minimises impacts on property from flooding;

(e) minimises disruption to residents, business or site operations and recovery time due to flooding;

(f) minimises the need to rebuild structures after a flood event greater than the defined flood event.

Note—Where Table 8.2.11.3.C identifies that a flood risk assessment is required, compliance with this performance outcome can be achieved by submitting a flood risk assessment, which may be included within a flood study, addressing the criteria within this performance solution. Preparing flood risk assessments and flood studies is required to be in accordance with the Flood planning scheme policy.

Note—An emergency management plan prepared in accordance with the Flood planning scheme policy, which sets out procedures for evacuation due to flooding may be used to demonstrate compliance with this performance outcome.

AO3

Development for a material change of use is identified in Table 8.2.11.3.C as compatible with the flood hazard in the relevant flood planning area.

PO4

Development for a park ensures that the design of a park and location of structures and facilities responds to the flood hazard and balances the safety of intended users with:

(i) the development design, siting and any mitigation measures will ensure the development is structurally adequate to resist hydrostatic, hydrodynamic and debris impact loads associated with flooding up to the defined flood event; and

(ii) the risk to people is managed to an acceptable level.

PO6

Development involving essential electrical services or a basement storage area is suitably located and designed to ensure public safety and minimise flood recovery and economic consequences of damage during a flood.

(b) if a basement contains essential electrical services or a private basement storage area, the basement is a waterproof structure with walls and floors impermeable to the passage of water with all entry points and services located at or above the relevant flood planning level in Table 8.2.11.3.D.

Note—A basement storage area does not include a bike storage room, change room, building maintenance storage and non-critical electrical services.

AO6.2

Development involving a basement that relies on a pumping solution to manage floodwater ingress or for dewatering after a flood provides a secondary pump system with a backup power source for the pump.

PO7

Development does not directly or indirectly create a material adverse impact on flood behaviour or drainage on properties that are upstream, downstream or adjacent to the development.

AO7.1

Development:

(a) does not block, or divert floodwaters for any area affected by creek/waterway or overland flow flooding, excluding storm-tide flooding and Brisbane River flooding sources; or

(b) does not result in a material increase in flood level or hydraulic hazard on upstream, downstream or adjacent properties.

Development retains existing overland flow paths and does not rely wholly on piped solutions to manage major flows.

AO7.3

Development which creates a new overland flow path or significantly modifies an existing overland flow path via earthworks does not materially worsen hydraulic hazard on the site from existing conditions.

Development for filling or excavation in an area affected by creek/waterway flooding does not directly, indirectly or cumulatively cause any material increase in flooding or hydraulic hazard or involve significant redistribution of flood storage from high to lower areas in the floodplain.

Note—This part of the code applies to all development other than a dwelling house and any secondary dwelling which involves filling or excavation, whether or not the development application comprises a separate development application for operational work involving filling or excavation.

AO8

Development ensures that no filling or excavation greater than 100mm is located in the Creek/waterway flood planning area 1, 2 or 3 sub-categories if contained in the 5% AEP flood extent of any Creek/waterway flood planning area sub-category for which no waterway corridor has been mapped in the Waterway corridors overlay.

(b) ensures floodwaters and flood debris can pass predominantly unimpeded under a structure or building to minimise property or building damage, including for a flood larger than the defined flood event;

(c) mitigates flood impacts by ensuring that filling, excavation and location of services are designed to allow for the conveyance of floodwater across the site.

(b) support efficient emergency services access and site evacuation with consideration to the scale of development.

Note—A flood risk assessment may be required to address the performance outcomes or acceptable solutions which deal with evacuation and isolation arrangements, and the ability to take refuge. The Flood planning scheme policy provides information for undertaking flood risk assessments.

Development involving a new road, a bridge or culvert is designed to minimise impacts to flood behaviour, minimise disruption to traffic during a flood and allow for emergency access.

AO12

Development involving a new road complies with the flood planning levels in Table 8.2.11.3.F.

PO13

Development for pedestrian and cyclist paths:

(a) provides a suitable level of trafficability;

(b) manages the impacts of flooding on asset life and ongoing maintenance costs;

(c) balances route availability with recreational and transport connectivity benefits to the city.

AO13.1

Development for cyclist and pedestrian facilities other than on public roads, including those traversing through a park and adjacent to a watercourse and overland flow path, are located above the 39% AEP (2 year ARI) flood immunity from all flooding sources.

Note—If the site is subject to more than one type of flooding, the requirement that affords the greatest level of protection will apply.

AO13.2

All new on-road cyclist and pedestrian facilities comply with the flood planning levels and trafficability standards for the applicable category of road in Table 8.2.11.3.F or Table 8.2.11.3.K.

PO14

Development which increases the residential population within the Brisbane River flood planning area sub-categories minimises the risk to people in all flood events with consideration to flood hazard, including warning time.

AO14

Development in the Brisbane River flood planning area sub-categories in areas where the residential flood level is greater than 12.8m AHD involving:

(a) an increase in the number of residential dwellings; or

(b) additional residential lots

is not subject to an unsafe hydraulic hazard in the 0.2% AEP flood event.

(a) remains functional to serve community need during and immediately after a flood event, or is part of a network that is able to maintain the function of the essential community infrastructure when parts of the development are unable to function during or after a flood;

(b) is designed, sited and operated to avoid adverse impacts on the community or the environment due to the impacts of flooding on infrastructure, facilities or access and egress routes;

(c) is able to remain functional or is part of a network which is able to remain functional even when other infrastructure or services (such as electricity supply) may be compromised in a flood event;

(d) contains mitigation measures which are not entirely dependent on human activation to respond to a flood event.

Note—Protection of function is required up to and including the flood event in Table 8.2.11.3.G.

Development which creates a new residential lot in an area subject to Brisbane River flooding, if the residential flood level is greater than 12.8m AHD is not subject to a hydraulic hazard greater than 0.6m2/s DV or 0.6m deep in a 0.2% AEP flood.

Development involving reconfiguring a lot creating more than 6 residential lots or a lot for industry ensures the flood planning levels of a dedicated road fronting the development or providing primary access within 200m of the development:

(3) Basement car parks must be suitably waterproofed and all air vents, air-conditioning ducts, pedestrian access and entry and exit ramps into the basement must comply with the applicable flood planning levels in this table.

(4) A shelter for a motor vehicle, which has a roof and one or more open sides, and which can be built against the side of a building.

(5) A slight or rough structure built for shelter and storage; or a large strongly built structure, often open at the sides or end.

(6) Where essential electrical services are proposed in a basement below the specified flood planning level, the flood immunity of all air vents, air-conditioning ducts, pedestrian access, lift shafts and entry/exit ramps at the basement entrance and any other openings into that basement must conform with the flood planning levels for Category A for Residential development, and the relevant basement entry level of all other uses. To ensure flood immunity,basements require a waterproof basement design to prevent flood waters entering the basement.

A flood event with an AEP of 2% is the equivalent of a 50 year ARI flood event.

A flood event with an AEP of 0.2% is the equivalent of a 500 year ARIflood event.

Where a building has a combination of uses that includes a component of classes 2, 3 or 9, the essential services for that building shall comply with the requirements of the building class with the greatest flood planning level requirement.

Use classes for residential development also include basement storage.

Lowest floor level is to be 2.5m(2) above the highest ground elevation in undercroft area

Creek/waterway (Flood planning area 1, 2 or 3 sub-categories)

Lowest floor level is to be 2.5m(2) above the highest ground elevation in undercroft area

Creek/waterway (Flood planning area 4 sub-category)

Lowest flood level is to be 1.5m (2) above the highest ground elevation in undercroft area

Notes—

(1) The minimum undercroft only relates to the minimum clearance requirements from ground level to the finished floor level and not minimum flood planning levels. Where the flood planning level requirement with freeboard results in a higher finished floor level that higher level needs to be adopted.

(3) A risk management approach determining flood planning levels of roads for Brisbane River flooding can be applied as an alternative to Table 8.2.11.3.F. Typically such roads would have a flood immunity no worse than the surrounding roads that support a similar land use, otherwise a Flood Risk Assessment which complies with the relevant requirements of the Flood planning scheme policyis provided.

No specific recommended level but development proponents should ensure that the infrastructure is optimally located and designed to achieve suitable levels of service, having regard to the processes and policies of the administering government agency.

(1) Where the site is subject to more than one flooding source, the minimum flood planning level is the highest level determined from these sources.

(2) Where flood levels are not available from Council's FloodWise Property Report such as overland flow flooding a suitably qualified Registered Professional Engineer in Queensland with expertise in undertaking flood studies is required to estimate the relevant flood level. The Flood planning scheme policy sets out the requirements for a flood risk assessment process.

(3) The design standard for industry access is the 5% AEP flood level for all flooding sources.

(1) Where the site is subject to more than one type of flooding that is overland flow flooding, creek or waterway flooding or river flooding, the minimum flood immunity level is the highest level determined from these sources.